When an internal combustion engine is shut off, unburned hydrocarbon fuel vapors may be left in the air induction system, engine cylinders, engine crankcase, etc. These hydrocarbon fuel vapors may migrate out of the engine cylinders through an open intake valve into the intake manifold along with vapors that have migrated from a crankcase to the intake manifold through a PCV (Positive Crankcase Ventilation) system. After the engine is shut off, the vapors may travel through the fresh air intake system and into the surrounding atmosphere. Further, vapors may also migrate from a crankcase, through a crankcase fresh air hose, to the fresh air intake system and then out into the surrounding atmosphere. Changes in ambient air temperatures may further encourage hydrocarbon fuel vapors to migrate from the vehicle.
To reduce the escape of hydrocarbon vapors from the engine air induction system (AIS), some vehicles include a hydrocarbon trap in the AIS having one or more hydrocarbon adsorbing surfaces to adsorb vaporized hydrocarbons during engine off soaks. These AIS hydrocarbon traps may be periodically purged of the temporarily stored hydrocarbon vapors when the engine is restarted and the vapors are inducted into the cylinders along with fresh air and consumed during normal engine combustion.
A flow-through hydrocarbon trap is positioned such that substantially all the vapors emanating from inside the engine during engine off soaks must pass through it before reaching atmosphere. A bypass hydrocarbon trap is also positioned in the vapor flow path, but only a portion of the vapors pass by or through it prior to reaching atmosphere. Although the flow-through trap is generally more efficient at reducing the amount of hydrocarbon vapors emitted to the environment, a bypass trap may be used to further reduce the escape of any vapors that pass through the flow-through trap, or that may bypass the flow-through trap based on the design of the AIS for some applications. A bypass trap may be used alone or in combination with one or more flow-through traps and/or bypass traps.
Various types of AIS flow through and/or bypass hydrocarbon traps are described in commonly owned U.S. Pat. Nos. 8,191,539; 7,458,366; and 6,905,536, for example. While suitable for various applications, these approaches may require a unique design for each application. Unique designs require additional engineering and development resources and fail to leverage available economies of scale afforded by a design that is more easily adapted to multiple applications. For example, previous designs may require different dimensions for different applications. Similarly, considerations relative to the engine volume may require more or less absorber channel openings. Many prior AIS hydrocarbon traps are difficult to scale and/or package within a vehicle due to space limitations and size and material constraints.